1. Field of the Invention
This invention relates to a method for making cellular glass, and more particularly, to a method for forming a fluidized bed of sintered particles within a fluidizing vessel and heating the fluidized bed of sintered particles to a cellulation temperature to cellulate the sintered particles to form discrete cellular glass nodules.
2. Description of the Prior Art
The use of cellular glass as a thermal insulating material is well known. Cellular glass thermal insulation has many advantageous features when compared with other types of thermal insulation. Cellular glass is an inorganic closed cell, lightweight material that has a high resistance to fire, moisture, vermin and other objectionable agencies and has desirable insulating properties that make it particularly suitable for use as insulating material and other useful products.
U.S. Pat. No. 2,691,248 discloses a method for forming cellular glass nodules where pellets of crushed glass and cellulating agent are introduced into a furnace. The furnace includes a sintering zone and a cellulating zone. The pellets are first passed through the furnace sintering zone and heated to a temperature sufficient to sinter the pellets. The pellets continue through the furnace cellulating zone and are heated to a temperature sufficient to cellulate the sintered pellets. The furnace comprises a rotary kiln type so that the pellets are rolled about during processing to retain a relatively spherical shape. As an alternative method for forming cellular glass nodules, the pellets of crushed glass and cellulating agent are first introduced into a sintering furnace and therein heated to a temperature sufficient to cause the pellets of crushed glass and cellulating agent to soften and coalesce into a sintered mass. The sintered mass is removed from the sintering furnace and allowed to cool, and then crushed into sintered particles of preselected size. The sintered particles are conveyed to a rotary kiln cellulating furnace and therein heated to a temperature sufficient to cellulate the sintered particles.
U.S. Pat. No. 3,441,396 discloses a method for making cellular material wherein calcined partially cellulated nodules are crushed and mixed with carbon in a conventional ball mill. The mixture from the ball mill is thereafter introduced into a conventional furnace mold, and the mold is placed in a furnace. The mixture is heated within the furnace to form buns or blocks of cellular material. As an alternative, the mixture of calcined partially cellulated nodules that have been crushed and mixed with carbon may be pelletized in a conventional pelletizer and thereafter introduced into a rotary kiln furnace. The pellets are heated within the rotary kiln furnace to form cellular nodules. The cellular nodules are introduced into a cooling lehr and cooled without thermal shock.
U.S. Pat. No. 3,532,480 discloses a method for making cellular glass sheets wherein a mixture of glass forming material and cellulating agent are agglomerated into pellets and heated to an elevated temperature so that the pellets partially cellulate. The partially cellulated pellets are made to cohere to each other to form a sheet of coalesced, partially expanded pellets. The sheet of coalesced pellets is fed into a heating chamber wherein the sheet of coalesced, partially expanded pellets is further heated to a cellulation temperature to form a sheet of cellular glass. As the sheet of coalesced, partially expanded pellets is passed through the heating chamber during the cellulation process, it is supported either on the surface of a molten metal bath or on a nonadhering surface of an endless conveyor belt.
While it has been suggested by the prior art methods to utilize either a rotary kiln furnace or a furnace including a molten metal bath or endless conveyor belt system to heat pellets to a cellulation temperature to form cellular glass, there is a need for an improved cellulation process wherein a fluidized bed of sintered particles is heated to a sintered particle cellulation temperature to produce cellular glass nodules. The fluidized bed process must be capable of producing cellular glass nodules of uniform size and uniform cell structure. The temperature of the fluidized bed must be sufficient to cellulate the particles suspended in the fluidized bed.